1. Field of the Invention
This invention relates an electrographic recording apparatus and more particularly to the one which records images on a recording body by using electromagnetic toner.
2. Prior Art
In conventional electrographic recording apparatuses, such as disclosed in the Japanese Patent Application Publication No. 50557/1983, electromagnetic toner is stored in a hopper; a member to carry the toner is installed under the hopper and is moved with respect to the hopper; a number of independent electrodes are arranged along the width of the toner carrier member downstream of the toner carrier member; a magnetic field is generated to prevent the toner from flowing out from the electrodes at all times; the electrodes are applied with voltage to weaken the toner blocking force produced by the magnetic field so as to allow the toner to flow out onto the toner carrier member and thereby form a toner image. This method has an advantage of being able to use dry toner and to form an image directly on the toner carrier member with low voltages.
However, with this method, if perfect control is to be made of electromagnetic toner flow at the electrode, a magnet of the magnetic field generating means is required to be installed somewhat closer to the toner hopper away from the electrode end along the toner carrying direction.
When the magnet of the magnetic field generating means is located near the toner hopper, the magnetic flux produced by the magnetic field generating means does not necessarily concentrate on the electrode. This is not satisfactory for stably forming toner chains between the toner carrier member and the electrode. If the magnetic field is intensified to ensure stable formation of toner chains, this gives rise to another problem, i.e., the toner blocking force will become very strong preventing stable supply of toner to the recording area where the toner chains are formed.
Another example of conventional electrographic recording using electromagnetic toner is disclosed in U.S. Pat. No. 3,816,840.
The process and equipment described in the U.S. publication may be summarized as follows: a first drum electrode incorporating a magnet roll carries electromagnetic toner to the recording area where a large number of toner chains are formed; and a current is supplied to the toner chain electric circuits to produce a force opposing the upward force generated by the magnet roll and thereby form an image in the recording area.
With this technique, however, there are many toner chains formed in the recording area by the magnet roll's field and a current is commonly supplied to the electric circuits of the toner chains (the electric current corresponds to each of the elements of the image to be formed). Thus, supply of current to many toner chains results in many toner particles adhering to the recording member, making it difficult to produce an image in strict accordance with image signals. Especially when it is desired to increase the recording density of image to obtain high-quality image recording, this technique can hardly be said to be practical.